1. Field of the Invention
The present invention relates to a four-lamp vehicular headlamp system, more particularly to a vehicular headlamp having a discharge bulb mounted on a sub-beam reflector.
2. Description of the Related Art
Discharge bulbs can provide high-luminance illumination and are increasingly used as a light source for vehicular headlamps. Four-lamp vehicular headlamp systems can provide enhanced vision under illumination with sub-beams if the sub-beam reflectors are each fitted with a discharge bulb.
If a vehicular headlamp is fitted with a discharge bulb, a lighting circuit unit must be provided to light the discharge bulb by applying high voltage to it. In the conventional vehicular headlamp, the lighting circuit unit is provided below the reflector on which the discharge bulb is mounted. This means if the discharge bulb is mounted on a sub-beam reflector, the lighting circuit unit is provided below the sub-beam reflector.
FIG. 5 shows a half section of a conventional four-lamp vehicular headlamp system comprising a lighting compartment 106 formed of a lamp body 102 and a front lens 104, a main beam reflector 108M and a sub-beam reflector 108S placed side by side in the lighting compartment 106, and a discharge bulb 110 mounted on the sub-beam reflector 108S. If a lighting circuit unit 112 is provided below the sub-beam reflector 108S, the following problem occurs.
With the four-lamp headlamp system, the main beam or high beam is not lit when the illumination with the sub-beam or low beam is on and the space around the sub-beam reflector 108S in the lighting compartment 106 becomes hot by the heat generation from the discharge bulb 110 and the lighting circuit unit 112 while the space around the main beam reflector 108M remains cold. As a result, haze is most likely to occur on the inner surface of that portion of the front lens 104 which is in front of the main beam reflector 108M.
The present invention has been accomplished under these circumstances and has as an object providing a four-lamp vehicular headlamp system that has a discharge bulb mounted on each of the sub-beam reflectors and which yet is effectively protected against haze formation on the inner faces of the front lenses.
The present invention aims to attain the stated object by choosing a specific position for installing the lighting circuit unit.
That is, the present invention provides a vehicular headlamp comprising a lighting compartment formed of a lamp body and a front lens, a main beam reflector and a sub-beam reflector placed side by side in the lighting compartment, and a discharge bulb mounted on said sub-beam reflector, wherein a lighting circuit unit for lighting said discharge bulb is provided below said main beam reflector.
By the expression xe2x80x9cprovided below the main beam reflectorxe2x80x9d is meant that the position of the horizontal center of the lighting circuit unit does not coincide with the middle point between the optical axes of the main beam reflector and the sub-beam reflector but is offset toward the optical axis of the main beam reflector. As long as this condition is met and the lighting circuit unit is xe2x80x9cbelow the main beam reflectorxe2x80x9d, it may be provided either within or outside the lighting compartment.
As stated above, the vehicular headlamp of the present invention comprises a lighting compartment formed of a lamp body and a front lens, a main beam reflector and a sub-beam reflector placed side by side in the lighting compartment; although a discharge bulb is mounted on the sub-beam reflector, a lighting circuit unit for lighting the discharge bulb is provided below the main beam reflector, so under illumination with the sub-beam, the space around the sub-beam reflector in the lighting compartment becomes hot by the heat generation from the discharge bulb and the space around the main beam reflector also becomes hot by the heat generation from the lighting circuit unit. As a result, the temperature in the lighting compartment can be maintained generally uniform to ensure effective prevention of haze formation on the inner surface of the front lens.
The conventional vehicular headlamp has another problem peculiar to cold climates. During illumination with the sub-beam, snow deposited on that part of the front lens which is in front of the main beam reflector does not readily melt, so that when the sub-beam is turned off and the main beam comes on, the light reflected from the main beam reflector is not sufficiently projected ahead of the front lens that it becomes difficult to secure the intended luminous intensity distribution. In contrast, the design of the present invention permits the temperature in every part of the lighting compartment to rise during illumination with the sub-beam so that the entire surface of the front lens has a snow melting capability. As a result, when the sub-beam is switched to the main beam, the latter can provide an adequate luminous intensity distribution.
Preferably, the vehicular headlamp according to the present invention includes a passageway through which the heat generated from the lighting circuit unit is directed toward the front of the main beam reflector is formed in the lighting compartment. With this design, the efficiency with which that part of the front lens which is in front of the main beam reflector becomes hot during illumination with the sub-beam is sufficiently enhanced to produce a greater effect in preventing haze formation on the inner surface of the front lens and melting the snow deposited on that front lens.
The specific design of the xe2x80x9cpassagewayxe2x80x9d is not limited in any particular way. For example, if an extension reflector is provided in front of said both reflectors in said lighting compartment, the passageway can be provided by forming a cutout at the lower end of said extension reflector in front of the main beam reflector. By this design, the heat generated from the lighting circuit unit can be effectively directed to a site in front of the main beam reflector.
During illumination with the sub-beam, the corners at the lower end of the space around the main beam reflector in the lighting compartment tend to become colder than other areas to have a greater chance of haze formation. To deal with this problem, preferably, an air hole penetrating the lamp body is formed near its bottom at the end of the side where the main beam reflector is provided. With this design, atmospheric air is introduced into the lighting compartment via said air hole to provide an even greater anti-haze effect.